The bombing of Azaz, some 30 miles (50 kilometers) north of Aleppo, shattered the sense of control rebels have sought to project since they took the area from President Bashar Assad's army last month. Azaz is also the town where rebels have been holding 11 Lebanese Shiites they captured in May.
The attack came on the same day the U.N. released a report accusing Assad's forces and pro-government militiamen of war crimes during a May bloodbath in the village of Houla that killed more than 100 civilians, nearly half of them children. It said rebels were also responsible for war crimes in at least three other killings.
The long-awaited report by the U.N. Human Rights Council marks the first time the world body has referred to events in Syria as war crimes — on both the government and rebel sides — and could be used in future prosecutions against Assad or others.
It said the scale of the Houla carnage indicated "involvement at the highest levels" of Syria's military and government. The council also said the conflict is moving in increasingly brutal directions on both sides.
Also on Wednesday, the Organization of Islamic Cooperation, comprised of 57 member states, released a final statement from its two day summit in Saudi Arabia's Muslim holy city of Mecca urging support of the opposition. The statement did not mention suspending Syria's membership, but OIC Secretary-General Ekmeleddin Ihsanoglu told reporters after the summit that the organization had agreed to do so. The move is largely symbolic.